This invention relates to universal joints--in detail, to the field of tripod type universal joints--and particularly provides a novel type of holding construction for holding the ball rollers and the needle rollers of such a tripod-type universal joint.
A tripod-type universal joint is adapted to transmit power from an input shaft to an output shaft. In the tripod-type universal joint, a central hub connected with an input or output shaft has three cylindrical trunnions projecting therefrom in three directions at 120.degree. to one another. Each of these trunnions has mounted on it a ball roller which is movable axially along the axis of the trunnion to a certain extent, and is also able to rotate around the axis of the trunnion. The ball rollers are of a generally part-spherical external shape, and they engage in roller races formed in a barrel-shaped element, which is integrally formed with an input or output shaft. The ball rollers can roll to and fro in these ball races.
Especially in the case of such a tripod-type universal joint which is used as an elongatable, constant velocity universal joint, between the trunnions and the ball rollers are placed needle rollers in order to facilitate the smooth rolling of the ball rollers on the trunnions. In this case, at the end of each of the trunnions is included a holding construction so as to retain the needle rollers and ball rollers on the trunnions. As long as the ball rollers are engaged in their respective roller races, in usual use of the joint there is no likelihood that they should come off their trunnions; but during assembly it can be very difficult to assemble the entire joint without some such holding device to facilitate the work and to prevent damaging the delicate needle rollers. Such a holding device, of course, must not hinder the necessary axial movement of the ball rollers along their trunnions which is required during usual operation of the universal joint. Such axial movement is quite small, however, since this sort of universal joint is not appropriate for transmitting power around sharp angles.
Several kinds of holding construction have been suggested to do this job. None of them, however, has been fully satisfactory.
A first holding construction was proposed one which includes an annular retainer which fits around the outer cylindrical surface of the trunnion. This has a needle roller stop face which opposes the ends of the needle rollers remote from the central hub, and a ball roller stop face which opposes the end of the ball roller remote from the hub. This retainer is held on the end of the trunnion by a circlip which is fitted into a groove formed around the end of the trunnion, and which projects from this groove. In this case, the outer part of the circlip engages a step formed at a middle portion of the inner peripheral face of the retainer (so that the inner radius of the portion of the retainer which is closer to the hub is less than the inner radius of the portion of the retainer which is further from the hub) and prevents it coming off the trunnion. Therefore, to assemble such a holding construction, it is necessary to push the retainer further onto the trunnion than its usual position during operation, in order to be able to fit the circlip into the groove on the trunnion. This requires that the needles are formed correspondingly shorter, thereby increasing the load pressure applied to the needles and the bearing surfaces of the trunnion and of the ball rollers. This presents a danger of damaging the delicate surfaces of the needle rollers, or the inner surface of the ball roller, during operation, and can reduce the working life of the universal joint drastically.
Another type of holding construction is known. In this, the ball roller stop face of the aforesaid retainer is provided as a set of flanges which may be elastically deformed. This permits placing the ball roller onto the trunnion after fitting the retainer to the trunnion by the circlip by elastically deforming the flanges. Of course, there is no problem in fitting the needle rollers after the retainer is fitted, since they can be approached sideways to their positions, in the absence of the ball roller. However, in this case, as all the needle rollers must be attached to the exterior cylindrical surface of the trunnion before fitting the ball roller, it is very troublesome to assemble the joint, and again, while the ball roller is being pushed over the elastically deformed flanges, there is a possibility that its internal annular cylindrical face, or the needle rollers, may be damaged, especially in view of the force required.
Again, there is a type of holding construction similar to the aforesaid one, wherein the flanges are not elastically deformed out of the way of the ball roller, but are bent into position after the ball roller has been fitted. However, this bending introduces weaknesses into the retainer, again risks damaging the various parts, and is generally difficult and unsatisfactory.